Medical treatment of the spine often involves an injury or disease of an intervertebral disc, the fibrocartilaginous joint between two adjacent vertebrae. Frequently, treatment involves removing the natural disc and fusing the two adjacent vertebrae. A fusion cage frequently is used to promote fusion of two adjacent vertebrae. One or more anchors may be used to secure the cage to one or both of the adjacent vertebrae. In some cases, an intervertebral prosthesis like an artificial disc joint may be used instead of fusing the two adjacent vertebrae. With such prostheses, one or more anchors may be used to secure plates or other components to one or both of the adjacent vertebrae.
The anchors often used to secure a fusion cage or intervertebral prosthesis component to a vertebra may take many forms. For example, a screw may be threaded into a vertebra with the head of the screw holding the treatment device against the vertebra. Nails and other forms of pins also may be used. Generally, the use of such fasteners requires a relatively large incision to accommodate the approach angle needed to adequately insert the screws, nails, or pins through the treatment device and into the vertebra.